Catalytic fuel combustion apparatus and method

ABSTRACT

A flameless catalytic combustion apparatus includes a combustion chamber with a hydrogenous fuel inlet and a mass of catalyst in the chamber between the inlet and an outlet. Preferably the catalyst mass comprises porous pellet bodies supporting varying high and low concentrations of platinum family metals dispersed therein. For spontaneous starting of combustion the fuel is one of the lower alcohols and the high catalyst concentration is at the fuel inlet. The fuel may be in a container pressurized by air, or a lower ether or lower hydrocarbon which is also a fuel. Preferably separate, valved conduits from the fuel container first supply either atomized fuel droplets or air and fuel vapor to the high catalyst concentration for spontaneous ignition of combustion and vaporized fuel for continued combustion throughout the catalyst mass. The catalytic combustion apparatus may include a heat exchanger for fluids such as air, water or personal care foams and creams, or may be used in heating and cooking apparatus.

RELATED APPLICATION

This application is a continuation in part of my copending applicationof the same title, Ser. No. 561,591, filed Mar. 24, 1975 and nowabandoned.

BACKGROUND OF THE INVENTION

The present invention relates to heating systems in which a mixture of afuel vapor and air are burned flamelessly on the surface of a catalyst.The invention relates particularly to the rapid and efficient startingof the combustion of the fuel when both the fuel and the catalyst areinitially cold; i.e., at a temperature near room temperature or lower.

The catalytic oxidation of hydrocarbons, alcohols, and other chemicalsat elevated temperatures has been practiced efficiently for many yearsin industrial processes, and more recently in such applications as smallspace heaters fueled by propane. A characteristic of such applicationsis that they operate steadily for relatively long periods, and arestarted from an initially cold state only infrequently. Thus, thecatalytic space heater can be ignited with a match, and large industrialcatalytic systems can be brought slowly up to operating temperature byauxiliary heaters. Such systems would be more conveniently started by aself igniting catalyst.

For certain applications which might be most advantageously served bycatalytic heaters, however, the heating periods are very short and thesystem must be heated frequently from a cold start; hence very rapid andefficient initiation of combustion is mandatory, and an auxiliaryheating system for starting combustion is unacceptable. One suchapplication is the heating of shave foam or cosmetics dispensed from anaerosol can, where a few grams of material must be heated from 50° F. to80° F. in a period of 10 to 20 seconds, or less. In this case theheating system must be small and inexpensive, but capable of developinghigh heating intensities very quickly, and also capable of completelyburning the fuel without production of noxious combustion products. Itis also imperative that the system be highly efficient in converting andtransferring the heating value of the fuel into the fluid which is to beheated.

Experience has shown, however, that suitable fuels, such as hydrocarbonsand alcohols, when vaporized and mixed with air, will not start to burnspontaneously when brought into contact with catalysts of the typescommonly used, unless the catalyst or the fuel, or both are preheated.

A further difficulty encountered in the use of conventional catalystresults from the fact that the catalytically active metal, for exampleplatinum black, is most effective when supported upon highly porous basematerials such as gamma alumina or silica gel, which are highlyhygroscopic. Thus, between heating periods when the system is cool, thecatalyst support material adsorbs moisture from the ambient air whichgreatly reduces the activity of the catalyst. This will completely blockthe spontaneous oxidation of preferred fuels such as methanol on thesurface of the catalyst when both catalyst and fuel are initially cold.

It is also highly desirable that catalytic heating systems forapplications such as those mentioned above use a fuel whose vaporpressure is higher than atmospheric so that a high velocity jet of fuelvapor can be used to aspirate the air required for combustion, thusavoiding the need for pumps or other pressurizing devices. Thus, puremethanol, one of the most easily catalytically oxidized fuels cannot beused without some pressure generating device. Hydrogen, another fuelwhich is readily oxidized catalytically, is not as practical in theseapplications because of the difficulties and cost of storing andhandling this gas under high pressure.

Accordingly, objects of the present invention are to provide apparatusand a method for rapid, spontaneous ignition of catalytic combustionwith a liquid fuel, preferably an alcohol, which is effective at lowtemperature relative to operating temperature and in the presence ofmoisture in the catalyst mass.

A further object is to provide catalytic combustion with high efficiencyof fuel utilization and without production of noxious combustionproducts.

STATEMENT OF THE INVENTION

According to one aspect of the invention catalytic fuel combustionapparatus comprises a combustion chamber forming a fuel inlet and anoutlet and a combustion path there between, and a fuel- andair-permeable mass of catalyst in the chamber the mass including arelatively high catalytic concentration at the inlet and a relativelylower catalyzer concentration toward the outlet.

Further according to the invention the apparatus comprises a containerof hydrogenous fuel connected by conduit means to the inlet to thecombustion chamber. Preferably the container holds fuels in both liquidand vapor phases supplied to the chamber in both phases.

Still further according to the invention the fuel is supplied in onephase for spontaneous ignition and in the other phase for extendedcombustion.

DRAWINGS

FIG. 1 is a schematic showing fluid heating apparatus with catalystpellets according to the invention;

FIG. 2 is a table of catalyst pellet symbols as used in the figures;

FIG. 3 is a cross-section of a highly concentrated catalyst pellet;

FIG. 4 is an elevation shown partly in section of apparatus for rapidheating of a personal care fluid;

FIG. 5 is a schematic showing of a heating plate combustion system usingair pressurized fuel;

FIG. 6 is a Heating Intensity versus a Fuel Mass Flow Rate Diagram; and

FIG. 7 is an elevation like FIG. 4 showing a modification thereof.

DESCRIPTION

Two-Phase Fuel Combustion--FIG. 1

Fuels

Catalysts--FIGS. 2 and 3

Fuel Flow Rate--FIG. 6

Lather Heater--FIG. 4

Stove--FIG. 5

Multiple Fuel Containers--FIG. 7

Two-Phase Fuel Combustion--FIG. 1

The catalytic combustion apparatus of FIG. 1 comprises a tubular metalcasing 1 having an upper fuel inlet 2 and a lower combustion productoutlet 3 covered by screens 4. Surrounding the combustion chamber withinthe casing 1 is a coil of metal tube 6 with an entrance 7 and exit 8 fora fluid to be heated. The remaining volume within the chamber is filledwith a bed of catalyst pellets 10 of three types 10A, 10B, 10C as shownin FIGS. 2 and 3.

Fuel is supplied to the combustion chamber 1 from a pressurizedcontainer 11 holding a hydrogenous fuel in liquid phase volume 12 andvapor phase volume 13 as described more fully under the caption Fuels.Fuel from the liquid volume is fed to a conduit 14 through a meteringvalve 16 whose rotating plug 17 has a space 18 for holding apredetermined amount of fuel which is released into the conduit upon 45°counter clockwise rotation of the plug from the position shown inFIG. 1. The metering valve plug 17 is coordinated with the plug 22 of avapor valve 21 by a mechanical coupling 19. The vapor valve plug 22,upon 90° rotation from the position shown, connects the vapor volume 13with a vapor conduit 24.

The liquid fuel conduit 14 leads to an atomizing nozzle 26 within an airaspirator 27, the nozzle spraying the metered amount of liquid fuel infine droplets toward the fuel inlet 2 to the combustion chamber 1.Immediately inside the inlet is a mass of catalyst pellets 10A with ahigh concentration of catalyst in the platinum family described morefully hereinafter under the caption Catalysts. A hydrogenous fuel suchas methanol will spontaneously ignite in flameless combustion on contactwith a high platinum family concentration, and thus the nozzle 26comprises means to initiate combustion at the inlet 2. Simultaneouslywith, or shortly after ignition fuel in vapor phase is supplied throughconduit 24 to a nozzle 20 with an orifice 25 which meters the continuousflow of vapor and directs it in a jet 28 through the convergence 29,throat 31 and divergence 32 of the aspirator toward the fuel inlet 2 tothe combustion chamber. The vapor jet entrains air and draws it throughopenings 32 adjacent the metering nozzle 20, mixing the fuel and air asthey approach the combustion chamber so that flameless catalyticcombustion is sustained by continued flow of the fuel in its vaporphase.

Heat from the combustion is exchanged with fluid flowing through thecoil 6, which fluid may be a gas such as air or a liquid such as water,either of which can be circulated through radiators or other apparatus.

A catalytic heater of the type described above and having a doublehelical coil as shown in FIG. 4 was tested to determine itscharacteristics as a water heater. For this purpose, the inlet wasconnected to a water source which provided a constant water flow rate of1.38 grams per second. The measured temperature rise of the water was12.8° C. The total volume of the catalytic heater, i.e. the catalystbed, was 8.05 cubic centimeters. The heating intensity of this systemwas thus 2.2 calories per second per cubic centimeter or in other units890,000 BTU per hour, per cubic foot. The importance of this highheating intensity can be visualized in terms of a familiar applicationsuch as a house heater which might typically have a capacity of 150,000BTU per hour. The catalytic heater described above scaled to a capacityof 150,000 BTU per hour would occupy a volume of only 0.169 cubic foot.Along with this remarkable heat intensity the heater operates with highefficiency and fuel economy, and low pollution in its combustionproducts.

Fuels

Of the many available fuels only four are known to ignite spontaneouslyand safely in the presence of a suitable catalyst at normal ambienttemperature, that is 40° to 100° F. Other fuels such as formaldehyde,formic acid and hydrazine hydrate will oxidize spontaneously but aretoxic, inconvenient and dangerous to handle. These safe spontaneouslyigniting fuels are hydrogen and the three lower alcohols, methanol,ethanol and isopropanol, methanol being preferred. While otherhydrocarbons such as natural gas or the lower alkanes may be used as aprimary fuel after ignition they will not start catalytic combustionspontaneously. Thus either in industrial processes using primary fuelsafter ignition or in intermittently started catalytic combustionapparatus using the starting fuel as an operating fuel also, the loweralcohols are useful.

Whereas primary fuels are delivered from a pressurized system, smallerapparatus run on the starting fuel requires fuel pressurization by airor a self pressurizing fuel. For catalytic combustion the lower ethers,dimethyl and methyl ethyl ether, and lower alkanes and alkenes have beenfound to be most suitable as a pressurizer when mixed with the loweralcohols. The mixture of methanol and dimethyl ether as a catalytic fuelis mentioned generally in U.S. Pat. No. 2,764,969 to Weiss. Such a fuelmixture has, however, been found to have a rather critical range ofalcohol ether proportion, particularly in small fuel containers used inportable or compact self-igniting combustion units such as are describedherein. While the ether is a fuel, the alcohol which is essential tostart combustion has a substantially lower vapor pressure, so that asfuel is withdrawn from the vapor space of a fuel container theconcentration of ether in the liquid phase drops resulting in a drop ofvapor pressure. When the pressure is reduced to the point that theheating rate is below the useful limit a residue of unusable fuelremains in the container. When the pressure drops to atmospheric theliquid residue is substantially all alcohol. I have found that if thealcohol is in excess of 25% by volume of the initial alcohol-ethermixture an unusable residue of fuel in excess of 35% of the originalfuel volume will result in substantial economic waste. On the other handa proportion of approximately 5% alcohol by volume is required to insurespontaneous ignition. Within the range of 5% to 25% alcohol (e.g.methanol) to 95% to 75% ether (e.g. dimethyl ether) 10% alcohol and 90%ether is preferred.

Although the loss of pressure and waste of alcohol could be avoided bywithdrawing fuel from the liquid volume 12 of the container 11, theliquid fuel would be evaported in the aspirator 27 or in the mass 10 ofcatalyst pellets. Such fuel evaporation produces a refrigeration effectwhich will reduce or inhibit ignition or continued combustion. However,according to one aspect of the invention, metering only a small amountof alcohol-rich liquid fuel does not inhibit spontaneous ignition, andsubsequently supplying fuel pre-evaporated in the fuel container 11isolates the combustion chamber 27 from the refrigeration effect. Thefuel container can absorb and dissipate the refrigeration remotely fromthe combustion chamber. Further the fuel container has sufficient massand external heat transfer surface to prevent excessive chilling of thefuel therein.

While the alcohol-ether pressurizer mixture described above has beenfound to be a reliable starting and running fuel, particularly in asingle fuel container delivering the fuel in liquid and vapor phase,several advantages have been found in the use of lower alkane, alkeneand cyclo hydrocarbons with less than five carbon atoms as a pressurizerfor the alcohols and as a primary, separately supplied fuel forcontinued catalytic combustion after spontaneous ignition with a loweralcohol-fuel mixture as described under the heading Multiple FuelContainers. Thus the preferred fuels for use in the present apparatusand method comprise not only ethers with less than four carbon atomsincluding dimethyl and methyl ethyl ether, but also the lower alkane andalkene hydrocarbons with a boiling point below nominal room temperatureincluding methane, ethane, propane including cyclo propane, butaneincluding n-butane and isobutane, ethylene, propylene, butene-1 and -2,butadiene and butylene including isobutylene.

As a pressurizing constituent of the lower alcohol starting mixture thelower hydrocarbons mentioned may comprise as little as 5% of the fuelmixture with 95% of the mixture rich in alcohol. As previously noted thealcohol may be as low as 5% by volume, but higher concentrationsapproaching 95% by volume are preferred because catalytic combustionwill start spontaneously more rapidly and reliably, particularly inhumid weather, if the starting fuel is rich in alcohol. A mixture of 60%methanol and 40% isobutane, for example, affords reliable starting inambients of 90% relative humidity, and at temperatures below 40° F.

Other advantages of using the lower hydrocarbons as a pressurizer forthe alcohol are that they are readily available at low cost and areaccepted as safe for personal use for example in cigarette lighters. Thelower hydrocarbons are quite compatible with the plastic lining materialcommonly used in pressurized dispensing containers. They do not formformaldehyde on combustion, have a low latent heat of vaporizationrelative to the lower ethers, and a substantially higher heat value.

When the ignition starting alcohol mixture and a primary fuel suppliedsimultaneously with or after ignition are in separate containers thestarting material can be richer in alcohol and quicker and more reliablefor spontaneous catalytic ignition if one of the lower hydrocarbons isused as a pressurizer, and the primary fuel for continued combustionafter ignition need contain no alcohol and therefore will maintain itspressure until all liquid is expended.

Catalytic combustion apparatus using lower hydrocarbons as a pressurizerand a primary fuel is described hereinafter under the caption MultipleFuel Containers--FIG. 7.

Catalysts--FIGS. 2 and 3

A platinum family catalyst is necessary for spontaneous ignition of ahydrogenous fuel. The platinum family includes the platinum group ofmetals platinum, iridium and osmium, and the palladium group ofpalladium, ruthenium and rhodium. Preferably the platinum familycatalyst is supported on a catalytically active porous body composed ofone or more of the porous forms of the group alumina, silica, zirconia,thoria and molecular sieves. The porous catalytic supports arerelatively inexpensive whereas platinum family metals are veryexpensive. Therefore, catalytic bodies have very little platinum familymetal. Porous catalytic pellets with a platinum content of approximately0.05 to 0.2% by volume are used in industrial processes which arebrought to combustion temperature but which cannot initiate spontaneousignition. Similarly the above named porous bodies cannot alone initiatespontaneous combustion, and are, moreover, powerful adsorbers ofatmospheric moisture and fuel at ordinary temperatures. For example, abed of 0.1% platinum black supported on the surface of small (1/8 inch)spherical pellets of highly porous gamma alumina, after several hours ofexposure in a combustion chamber to air of normal humidity, will notcatalyse the oxidization of an air-methanol fuel at room temperature.Nor will such a catalytic body initiate spontaneous combustion of liquidor vapor phase fuel mixture of 5% to 25% methanol in dimethyl ether.

I have found that the ignition inhibiting effect of adsorbed moisture isovercome by substantially increasing the platinum family content of theporous catalytic body to at least approximately 2% and in a range up to60% of the initial weight of the porous body.

Below approximately 2% spontaneous ignition does not occur. Above 60%the time for combustion to start increases markedly. Within the range of2% to 60% platinum, a platinum content of 18% to 50% of the initialporous body weight assures the fastest starting of spontaneous ignition.

Catalytic bodies with such a high platinum family content are, ofcourse, relatively costly but I have further found that only a smallproportion of the catalyst bed 10 within the combustion chamber 27 needconsist of the enriched or highly concentrated 2% to 60% platinum familybodies 10A, symbolized by cross hatched areas in FIG. 2, and that lesscostly platinized porous bodies 10B with under 2% platinum familyconcentration symbolized by shaded areas in FIG. 2, and unplatinizedporous bodies symbolized by unshaded areas in FIG. 2, may be used as themajor portion of the catalytic mass 10.

The preferred form of enriched catalytic pellet is a porous support ofgamma alumina with 2% to 60% platinum black or palladium superficiallydispersed in the alumina as shown in FIG. 3.

The lower (under 2%) platinum family concentration bodies 10B mayconsist of platinum applied to the surface of gamma alumina pellets.

The unplatinized catalytic pellets 10C are preferably porous gammaalumina.

As described in more detail under the caption Lather Heater--FIG. 4 thebodies 10A of high catalytic concentration are disposed at the fuelinlet 22 to the combustion chamber 1 where they will initiatespontaneous combustion despite the fuel refrigeration effect and thepresence of adsorbed moisture.

Starter pellets 10A, although exposed to humid air for days will ignitecatalytic combustion within a few seconds when exposed to methanol.Combustion will then dry and spread through the bed to less enrichedpellets.

Fuel Flow Rate--FIG. 6

A precaution should be taken with catalytic apparatus to avoid unwantedand toxic products of combustion such as the adlehydes corresponding tothe alcohols and ethers in the fuel, for example formaldehyde.Formaldehyde can be detected by its odor when present in non-toxicquantities of a few parts per million and therefore detection by odor isa practical and safe test. Above a barely discernable odor formaldehydeis very irritating to the eyes and nose. If formaldehyde formation isavoided other toxic or irritating oxidization products such as carbonmonoxide, ethers or organic acids are also avoided.

I have found that such unwanted products of combustion are avoided ifthe dimensions of the apparatus are selected such that one or both oftwo parameters called Heating Intensity and Fuel Mass Flow Rate are keptwithin critical limits. These parameters are defined as follows:

Heating Intensity is the heating power absorbed by the heat exchanger,divided by the volume of the space occupied by the catalyst. Convenientunits in which to express Heating Intensity are [calories/(sec×cm³)].

Fuel Mass Flow Rate is flow rate of the fuel vapor, divided by the crosssection of the catalyst bed through which it flows. Convenient units are[grams/(sec×cm²)].

In FIG. 6 Fuel Mass Flow Rate is compared to Heating Intensity withrespect to formaldehyde formation during catalytic combustion. Outsidethe shaded area substantial amounts of formaldehyde can be detected byodor when Heating Intensity exceeds 4.5 cal/(sec×cm³) or when Fuel Massflow rate exceeds 0.0025 gms/(sec×cm²). Within the shaded areaformaldehyde is not formed in detectable amount.

It is, of course, necessary to provide sufficient heat transfer surfacesuch that conventional surface heat transfer coefficients are notexceeded on either the catalyst side or the fluid side of the heatexchanger (e.g. coiled tubing 6 in FIG. 1), and that the correct ratioof fuel vapor and air is maintained for optimum oxidation. Typicaldimensions affording the two parameters, are given in the description ofLather Heater--FIG. 4 and Stove--FIG. 5. For complete combustion ofmethanol-dimethyl ether fuel from the vapor phase of the container 11 ofFIG. 1 the aspirator 27 should entrain about fifteen volumes of air toone volume of fuel vapor. An excess of air may produce formaldehyde andresults in excessive heat loss in the exhaust.

Lather Heater--FIG. 4

The present catalytic combustion apparatus being compact and requiring asmall fuel supply is particularly practical for heating, at dailyintervals for example, of personal care media or products such asshaving lather and skin creams which have enhanced effect when hot. Suchdevices must necessarily be reliable, safe and quick to heat the fluidproduct, i.e. in a few seconds. The fuel should be easily replaceable.

Shown in FIG. 4 is a hot shaving lather dispenser 40 embodying the fuelsupply and combustion chamber of the fluid heater of FIG. 1. A housing41 of transparent plastic material encloses and supports a metalcombustion chamber 1, fuel container 11 and aspirator 27 like thosedescribed with respect to FIG. 1 except that the heat exchange coil 6*is a double concentric helix. The coil 6* has an entrance at 7 outerturns winding downwardly toward the screen 4 chamber outlet 3, whenceits inner turns wind upward to the outlet 8. The coil may be aluminumtubing with an outside diameter of 0.3175 cm. and an inside diameter of0.254 cm., the outer turns being 2.857 cm. and the inner turns being1.588 cm. in outer diameter. The double helix coil is tightly wound andwith the turns close to or in contact with each other. Closely woundturns, preferably bonded together will serve to confine the catalystmass 10 between the inlet and outlet screens 4 without the externalchamber wall 1.

Spacers 42 extending from the housing 41 slidingly confine and insulatethe combustion chamber 1 which rests on a leaf spring 43 yieldinglyholding the chamber in the upper position shown. The aspirator 27 isrigidly attached to the chamber by a flange 44 crimped over a flange atthe top of the chamber. The nozzle 20* fixed to the top of the aspiratorcomprises a plunger sliding in a collar 46 formed by the housing 41.Depressing the nozzle-plunger 20* slides the aspirator-chamber assemblydownward against the spring 43. The entrance tube 7 of the coil 6*extends downwardly to a flare 47 receiving the stem valve 48 of anaerosol dispenser 49 of shaving lather or other personal care creamyfluid. The downward extension of the entrance tube 7 is sufficientlyrigid to open the stem valve 48 when the aspirator-chamber assembly isdepressed by the plunger 20*, thereby releasing shave or other creamthrough the heat exchange coil 6* to its outlet 8 and then through aspout leading out of the housing 41. During flow through the heatexchange coil the cream is heated to a suitable degree by flamelesscatalytic combustion of fuel in the chamber.

Fuel is supplied to the chamber from a pressurized container 11. Thefuel comprises 10% of a lower alcohol, preferably methanol, and 90% of alower ether pressurizer-fuel, preferably dimethyl ether, the fuelmixture having a lower liquid phase volume and an upper vapor phasevolume at approximately 3.5 Kg/cm² pressure above atmospheric. Apredetermined amount of liquid fuel, e.g. 0.050 ml., is released by ametering stem valve 16* functionally equivalent to valve 16 of FIG. 1. Acontinuous flow of fuel in vapor phase is released by an upper valve 21*functionally equivalent to valve 21 of FIG. 1. The lower stem valve 16*communicates with the atomizer nozzle 26 through a passage 52 in thebottom wall of the housing 41 and a flexible plastic tube 53. The upperstem valve 21* communicates through a passage 54 in a button 56telescoping over the stem valve 21*, and thence through a flexibleplastic tube 57 to a filter 58 within the nozzle 20*. The pressurizedfuel container 11 is replaceably and slidingly confined in a socket 59.Depressing the button 56 actuates both stem valves 16* and 21*approximately simultaneously, the container itself comprising amechanical link between the two. However, the internal spring of theupper stem valve may be stronger than that of the lower to delay openingof the upper valve 21* a fraction of a second after opening of the lowerstem valve 16*.

In use the button 56 is depressed opening the two valves 16* and 21*.Valve 16* delivers the methanol rich starting fuel droplets to theenriched pellets 10A at the inlet 2 to the combustion chamber causingspontaneous catalytic ignition. The button is held depressed for a few,e.g. 6, seconds until delivery of fuel vapor through the upper stemvalve 21*, nozzle 20* and aspirator 27 spreads combustion through thecatalyst bed 10. At the end of the combustion period a glow in thecombustion chamber can be seen through the transparent housing 41, andthe aspirator which may be made of heat resistant transparent plastic ormay include a light pipe 30 transmitting the glow of the catalyst bed.The nozzle-plunger 20* is then depressed for about 6 seconds to deliverabout 3 grams of hot cream to the spout 51 at about 80° C., the buttonbeing released about 2 seconds later.

In a lather heater of the type described the space occupied by catalystpellets was 4.97 cm³ with a section across the path of fuel flow of 2.61cm². The starter catalyst 10A at and near the fuel inlet 2 consisted of25 pellets of gamma alumina, each approximately 0.318 cm. in diameter,and superficially filled with platinum adding 40% to the initial weightof the gamma alumina. The balance of the catalyst space was filled withpellets 10B similar except that they had a low concentration ofapproximately 0.1% platinum by weight.

The aspirator 27 comprised a converging section 29 blending smoothlywith a throat 31 of 0.318 cm. diameter, which in turn blended with adivergence 32 whose total angle of divergence was 10° and whose widestdiameter was 2.22 cm.

The Fuel Mass Flow Rate was 0.0023 grams/(sec×cm²) and the HeatingIntensity was 3.8 cal./(sec×cm³). The combustion products contained noformaldehyde detectable by odor.

Stove--FIG. 5

In addition to the heat exchange systems of FIGS. 1 and 4 the presentcombustion apparatus is quite useful and efficient in the form of thestove plate or space heater shown in FIG. 5., particularly in a confinedspace such as a boat cabin where extra precautions against fire andnoxious fumes must be taken.

To reduce fire hazard a container 11* of alcohol (e.g. methanol) alonewithout a self-pressurizing additional fuel is pressurized as neededwith air supplied by a hand pump 61. The container has a liquid phasevolume 12 connected by a pipe 62 to a valve 64, and a vapor phase volume13 connected by a pipe 63 to the valve. The valve body 66 has a holdingspace 67 for a predetermined amount of fuel vapor. In this case analcohol rich vapor is effective to ignite spontaneous combustion whenthe valve body is turned 45° counter clockwise delivering thepredetermined amount of alcohol vapor through a pipe 68 to an atomizer69 also capable of converting liquid fuel into droplets. The valve body66 also has an elbow shaped passage 71 which upon rotation of the body90° more or less connects the liquid volume 12 and pipe 62 with a pipe72 leading through a catalyst bed 73 and a second valve 82 to a jetnozzle 76 like nozzle 20 of FIG. 1. The liquid fuel is vaporized inpassing through the ignited catalyst bed and entrains air in anaspirator 77. The aspirator leads to a folded combustion chamber formedby an upper, circular, metal hot plate 78, bottom and side insulatingwalls 79 and a metal partition wall 81. As is well known the hot plateis adapted to transfer a substantial amount of heat from the catalyticcombustion path, and thereby reduce the temperature of the combustinggaseous fuel as it flows toward an outlet now described. The plate andwalls define a combustion path with a fuel inlet 2* thence running firstoutwardly then inwardly to an outlet 3*. Here the combustion path isfolded over-and-under in a vertical plane, although it may be foldedside-by-side in a horizontal plane. In either case the outlet is inthermal conductive relation through the metal partition wall 81 with theinlet where high heating intensity due to the high catalystconcentration pellets 10A provides heat transfer to the pellets at theoutlet and affords more complete combustion and avoidance offormaldehyde formation. These advantages may be further promoted bydisposing a few high catalyst concentration pellets 10A at the outlet 3*filling the remainder of the combustion path with low catalystconcentration pellets 10B and with platinized gamma alumina pellets 10C.

While the lower alcohols, particularly methanol, are safe and efficientfuels for portable or mobile stoves and heaters, the stove of FIG. 5 maybe run on hydrocarbon fuels such as propane or natural gas if they areavailable. In FIG. 5 a gas main 83 also leads to the second valve 82.After ignition by alcohol from the container 11* the valve 82 may switchfuel supply from the container 11* to the gas main 83.

Multiple Fuel Containers--FIG. 7

The hot shaving lather dispenser 40* of FIG. 7 is identical inconstruction and operation with the dispenser 40 of FIG. 4 except thatthe socket 59* of FIG. 7 is adapted to receive two fuel containers 11Aand 11B in place of the single container 11 of FIG. 4.

The lower fuel container 11A contains an ignition starting fuel mixtureof a lower alcohol preferably with one or more lower alkanes or alkenesas pressurizer as described at the end of the section captioned Fuels.As much as 95% of the mixture may be alcohol which is supplied from theliquid mixture 12A occupying all but the top gaseous volume 13A withinthe container 11A. A predetermined amount of liquid alcohol rich fuel isreleased by a stem valve 16* like that of FIG. 4 and conducted throughthe tube 53 to an atomizing nozzle which forms and directs alcohol richdroplets on the starter catalyst pellets 10A at the fuel inlet 2 of thecombustion chamber 1 thereby spontaneously initiating catalyticcombustion.

The upper container 11B holds a pressurized fuel, preferably one of thelower ethers, alkanes or alkenes previously described. Its stem valve21* engaged by a button 56 is opened continuously while the button isdepressed whereas the stem valve 16* of the lower container 11A opensonly momentarily. The upper valve 21* may open simultaneously with orshortly after the lower valve 16*, and is held open a few seconds oruntil a glow can be seen in the catalyst bed 10. The upper valve 21*releases vaporized fuel through a tube 57 to a metering nozzle 20* whichdirects a jet of fuel vapor.

Whereas a two-phase alcohol-ether fuel is advantageous in the singlefuel container of FIG. 1, the alcohol-hydrocarbon starting mixture inlower container 11A and a hydrocarbon primary fuel in the separate uppercontainer 11B of FIG. 7 have the advantages in the low cost and readyavailability of accepted hydrocarbon fuels compatible with conventionalplastic container linings. The lower alkane and alkene hydrocarbons donot form formaldehyde and pressurizers allow a higher percentage ofalcohol in the starting mixture and have high heating value both as apressurizer in the lower container 11A and as a primary fuel in theupper container 11B.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

I claim:
 1. Catalytic heating apparatus with a combustion chamberwhereinthe combustion comprises:a fuel inlet, an outlet, a combustion pathbetween the inlet and outlet, a fuel permeable catalytic mass in thechamber on the path, a heat exchange wall adjacent the path adapted toextract a substantial quantity of heat from the catalyst mass and reducethe temperature of combustion gases flowing toward the outlet, said heatexchange wall being on one side of the path at the inlet and theconductive wall being on the other side of the path at the inlet, and athermally conductive wall folding the combustion path so that the inletand outlet are in heat exchange relation through said path folding wall,thereby to raise the temperature of combustion gases in the path at theoutlet by heat conduction from the path at the inlet.
 2. Apparatusaccording to claim 1 wherein combustion is started at said inlet and thewall heats catalyst at the outlet.
 3. Apparatus according to claim 1including means to initiate combustion at the inlet.
 4. Apparatusaccording to claim 1 wherein there a relatively high catalyticconcentrations at the inlet and a relatively lower catalyticconcentration toward the outlet.
 5. Apparatus according to claim 4wherein the wall separates the higher and lower catalyticconcentrations.